Application of the Quadrature Demodulation for the Measurement of Electric Power Parameters

Electric power can be divided into active, reactive and apparent power. The following parameters are used to estimate all types of electric power: power of fundamental spectral component, power of harmonics and the power in a given frequency band. To determine these parameters, the most effective method is based on the application of spectral analysis for voltage and current. The complex spectrum of signal is normally obtained using discrete Fourier transform or by quadrature demodulation. The quadrature demodulation technique allows a higher measurement accuracy. This article considers the application of quadrature demodulation for measuring complex spectrum, frequency, and power parameters. Analytical expressions of cross-correlation of the measurement errors and the parameters of the output filter are obtained. The application of moving average filter and a Butterworth IIR-filter as an quadrature demodulator output filter are considered. Simulation modeling was performed in Matlab.